1. Technical Field
This invention relates generally to wireless communication, and more particularly to methods and apparatuses for operating a power amplifier in a wireless communication system.
2. Background Art
Wireless communications devices employ circuits having power amplifiers. Power amplifiers are used to amplify, for example, transmission data signals for transmission through an antenna circuit. An ideal amplifier for wireless communications is linear and power efficient. Said differently, the input-output transfer function of a wireless communication power amplifier should be linear, with a perfect replica of the input signal, increased in amplitude, appearing at the output of the power amplifier. This output signal is then delivered to an antenna system for wireless transmission to other devices.
It is understood that efficiency of wireless communication systems can be enhanced when power amplifiers are run at—or near—their saturation levels. This means that the actual power output by the power amplifier is just below the maximum rated output power level. Output power is tied to the supply voltage of the power amplifier. Accordingly, a greater supply voltage will produce a correspondingly greater output power. For larger input signals, higher output power is required to run the power amplifier in saturation. Most prior art power amplifiers, however, used fixed power supplies. Since input signals can vary by orders of magnitude, fixed supply voltages are terribly inefficient and result in large current drain since the power amplifier is frequently not operating in saturation.
There has been some effort expended in constructing power supplies that vary the supply voltage that is applied to the power amplifier. Examples include power supply modulation, which varies the supply voltage by using a signal detector and a tracking power supply. However, prior art power supply modulation techniques suffer from problems. Illustrating by example, they tend to have poorer efficiency characteristics than fixed power supplies and sometimes can only be used in narrowband applications.
In contemporary broadband wireless communication applications, such as the 3GPP Long Term Evolution (LTE) project, practical considerations such as extending battery life set performance requirements on the operation of the power amplifier. The goal of these design considerations is to minimize power amplifier power consumption, cost, and complexity. Generally, required conducted power levels must be achieved within a specified lower bound on in-band signal quality, or error vector magnitude of the desired waveform, while staying below an upper bound of signal power leakage out of the desired signal channel or resource block allocation.
While the issues above represent traditional power amplifier challenges, they do not provide solutions. Further, to be commercially viable, it is advantageous for solutions capable of meeting the specification to be low cost and robust. Additionally, solutions must be capable of addressing issues not set forth in specifications, including being able to optimize when transmitting new waveforms, when transmitting packet based data in accordance with schedules dictated by new networks, and when transmitting across different frequency or spatial wireless communication technologies. This optimization should occur while maintaining adherence to the requirement standards as well. It would thus be advantageous to have an improved power amplifier circuit.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.